Reliability Analysis of LPCVD SiN Gate Dielectric for AlGaN/GaN MIS-HEMTs

In this paper, we investigate Low Pressure Chemical Vapor Deposition (LPCVD) SiN as a gate isolation material for AlGaN/gallium nitride (GaN) MIS-high electron mobility transistor power transistors. We compared the dielectric failure by forward-biased constant-current stress time-dependent dielectric breakdown measurements and statistical Weibull analysis. Several 4" AlGaN/GaN-on-Si wafers have been processed with different gate isolations and processes. Our investigation includes the dependence of the dielectric breakdown on the process flow (influence of dry etch), the thickness of the dielectric (12-20 nm), the area scaling, and the gate electrode, where we also consider the recently presented poly-silicon electrode. Additionally, we show the influence of the current density through the gate on the charge-to-breakdown characteristics as well as the influence of the temperature on the breakdown behavior. Using the polysilicon electrode and 20 nm LPCVD SiN as gate isolation, we achieved a charge-to-breakdown of QBD, 10 mA/cm 2 = 3.7 kC/cm 2 at T = 130°C for j = 10 mA/cm 2 . A 20-years lifetime (100 ppm, T = 130°C) extrapolation for a scaled area of 0.2 mm 2 (=WG = 100 mm) leads to a positive gate voltage of VG = 9.4 V.